The present invention relates to a stepping motor which is used in a dehumidifier, an insect repellent device or the like in such a manner to be able to realize a current reduction, a noise reduction and an extended life, and a fan incorporating such stepping motor therein.
Conventionally, there has been proposed an electric fan for use in a dehumidifier or the like (for example, see the patent literature 1-3, and 8). However, these conventional technologies do not take it into consideration to drive an electric motor by a battery and thus do not aim at realization of the reduced current, reduced noise and extended life.
In view of the above problem, to reduce the power consumption of the fan motor, there are proposed a technology which detects the effect of the fan motor and controls (reduces) the number or revolutions of the fan motor in accordance with the amount of the detected effect or drives the fan motor intermittently to thereby restrict the current consumption (for example, see the patent literature 4), a technology in which a fan motor is composed of a single blade using a piezoelectric element (for example, see the patent literature 5), and the like.
However, in the technology in which the fan motor is made of a single blade, there is necessary a booster circuit, which results in the expensive fan motor.
As a motor of a low current consumption type, there are known single-phase stepping motors for a clock (for example, see the patent literature 6 and 9). However, these stepping motors are very small in torque and thus it is difficult to apply them to a fan motor.
Further, in the patent literature 7, there is proposed a fan motor which uses a stepping motor as a drive source. However, in this fan motor, since the inertia moment of an impeller is large when the fan motor is driven with a low current, the fan motor cannot be started but is caused to step out. Therefore, it is difficult to drive the fan motor with a low current.
In addition, in the above patent literature 2 and 3, there are disclosed structures in which there is provided a fan receiving part in a motor shaft and a fan is driven by friction between the fan receiving part and fan. Use of such structure intends to stop the fan even during rotation of a motor when the fan device is inclined. In other words, the motor shaft and fan have a clearance between them in the radial direction; and, therefore, there is a possibility that the center of gravity of the fan can be deviated from the motor shaft, which can worsen the balance of the fan or can give rise to vibrations and noises.
In view of the above circumstances, conventionally, as a fan motor, there is used a DC motor with a brush in which the resistance value of a rotor is set large, whereby there is obtained a no-load current of several mA. However, since the DC motor is driven continuously for a long time, the life of the DC motor provides a problem. To solve this problem, it is also possible to use a brushless motor having no contact such as a brush, thereby being able to extend the life of the motor. However, in the brushless motor, only the Hall element thereof requires a current of several mA and thus, when electricity necessary for conduction of other drive circuits and motor is included, the necessary consumption current provides several decades of mA. As a result, for example, it is difficult to drive the brushless motor continuously for a long time using a battery.
There is known a sensor-less motor which includes no Hall element. In this motor, however, it is necessary to detect a coil back electromotive current and thus the motor must be high in the starting characteristic thereof. As a result, it is difficult to reduce the power consumption, so that the motor becomes expensive. When there is used a stepping motor requiring no Hall element, it is also possible to drive it with a reduced current. But, in this case, since the start torque of the motor is small, when driving and rotating an impeller and the like having large moment of inertia, the motor cannot be started but can be stepped out. That is, with use of such motor, it is difficult to drive the impeller with a low current.    Patent literature 1: JP-UM-H02-100631 publication    Patent literature 2: JP-H03-154613 publication    Patent literature 3: JP-H11-197438 publication    Patent literature 4: JP-H10-5622 publication    Patent literature 5: JP-2000-513070 publication    Patent literature 6: JP-S61-11390 publication    Patent literature 7: JP-H10-136634 publication    Patent literature 8: JP-H5-153892 publication    Patent literature 9: JP-H8-255859 publication